For the past year or so I've been working on and off on an adequate conversion Tool/Spreadsheet for PES Stats to FM Stats. The process for converting each attribute can essentially be boiled down to two parts; Using a formula to calculate the desired attribute, and then applying that number to the 1-20 FM Scale.
Certain attributes correspond with each other directly and dont require any intricate formulas (.i.e. Top Speed = Pace, Stamina = Stamina, Acceleration = Acceleration etc...) . But some do not have a direct counterpart, for these a formula is used that takes into account the relevant attributes as well as in some cases the players position(s), stars and/or player index cards (2011 format)..
For example.. the formula for crossing is (LPA*.8+LPS*.2), but this only applies to wide players and players that can play in wide positions. for players that can play in central attacking positions the formula is ((LPA*.8+LPS*.2)*.9), and for players than can only play in central defensive positions the formula is ((LPA*.8+LPS*.2)*.8).
Most of the mental attribute formulas are more complex and multi-layered than this, but the crossing formula is a good example of the general process.
there are number of ways that various attributes are then scaled for the 1-20 FM format.. the standard scaling is.
<=49 = 1
this applies to: Crossing, Finishing, First Touch, Heading, Long Shots, Passing, Penalty Taking, Tackling, Technique, Aggression, Anticipation, Bravery, Composure, Concentration, Decisions, Determination, Vision, Team Work, Acceleration, Agility, Balance, Jumping Reach, Natural Fitness, Pace, Stamina and Strength.
There is another method of scaling that is identical to the one above from 77 upwards, but scales down more harshly from that point downwards.
this applies to: Corners, Dribbling, Free Kicks, Flair, Work Rate and Jumping Reach. this is to correspond with the general pattern in how low these attributes are rated in FM on the lower end of the spectrum.
The defensive attributes (Marking, Tackling and Positioning) are scaled completely differently, as is Off the Ball. this corresponds with how Att and Def are scaled more drastically in PES.